1. Field of the Invention
The present invention relates to a data transfer method and a data transfer apparatus for making a robot perform desired operations in various driving axes in synchronism with each other.
2. Description of the Related Art
Generally, as a data transfer method for operating various axes of a machine tool or a robot in synchronism with each other, there is a known data transfer method in which a master unit, such as a controller situated on an upstream side and slave units, such as a plurality of servo amplifiers situated on a downstream side are connected in series by a daisy chain system with a serial bus, and data having an appended error check code or data having an appended error correction code are transferred from the upstream side to the downstream side. In a machine tool or the like having three mutually orthogonal axes, when a current position of a feeding axis is to be detected, the positions of the other axes must also be detected in synchronism. When one axis is to be moved, synchronism with other axes is also required.
Japanese Patent Publication No. H10-13394 (Patent Reference 1) discloses an example of such a data transfer method. In this example, a plurality of servo amplifiers are connected in series via communication lines such as optical cables to a numerical control apparatus by a daisy chain system. The numerical control apparatus transmits a position command or the like via the communication lines to various servo amplifiers, and various servo amplifiers receive the position command or the like. Each servo amplifier drives a servo motor in accordance with the received position command or the like. The control apparatus situated on the upstream side is adapted to receive feedback signals from slave units which include the servo amplifiers and servo motors.
Also, Japanese Patent Publication No. 2001-94626 (Patent Reference 2) discloses another example of a data transfer method. In this example, data can be transferred at high speed between a plurality of slave units, which are connected to a master unit. In other words, the data transfer apparatus is provided with a communication rank control portion and uses control lines provided separately in addition to a data communication line to determine whether or not the communication data should be transmitted.
However, with such a data transfer method, there is a problem that, when data having the appended error check code or data having the appended error correction code are to be transmitted from downstream individual slave units to the upstream side, the data transfer speed tends to be lowered. For example, in Patent Reference 2, a method is disclosed wherein a unit connected by a daisy chain system checks for errors in data received from another unit connected on the downstream side. With this method, data cannot be transferred to the upstream side until all of the data has been received, and this makes it impossible to transfer data at high speed. Therefore, the present applicant has proposed to increase data transfer speed by transferring data 51 having the appended error check code or error correction code without performing the error check of the data having the appended error check code or error correction code, as shown in FIG. 8. FIG. 9 is a view showing an example of another case where data are transferred in an opposite direction, i,e, from the upstream side to the downstream side.
However, in the example shown in FIG. 8, there is a problem in that error information from individual slave units 53 cannot be obtained from data having the appended error check code or error correction code received by the master unit 52, and it is impossible to identify the slave unit 53 where the error has occurred. In the example shown in FIG. 9, there is also a problem in that error information cannot be obtained from data 51 having the appended error check code or error correction code transmitted by the master unit 52 and received by a receiving slave unit 53, connected to the serial bus from the data transmitter to the data receiver, and it is impossible to identify the slave unit where the error has occurred. Therefore, when performing maintenance on the machine tool or the robot which is shut down by an error in control data caused by noise or fault, it takes a lot of time to detect the noise source or locate the fault, and maintenance cost may be increased due to unnecessary replacement of parts.